ESTRO 2025 - Abstract Book

S1343

Clinical - Lung

ESTRO 2025

Purpose/Objective: SBRT to lung metastases from colorectal cancer (CRC) has been applied to improve disease control in in the oligometastatic (OM) and oligoprogressive (OP) setting (LM). The aim of this study is to assess the impact of KRAS mutational (KRASmut) status in the response to SBRT in LM. Material/Methods: Data from a consecutive cohort of OM/OP CRC patients treated at our Institution with SBRT for LM from May 2019 to March 2024 were retrospectively reviewed. Statistical analysis was performed to correlate outcome with patient (age, KRASmut in primary tumor, OM/OP disease, prior chemotherapy lines) and treatment-related variables (dose regimen in Biologically Effective Dose: BED). Results: Sixty-two patients (median age: 74 years, range 49-85), accounting for 103 LM were included. LM were treated in the OM and OP setting in 65(63%) and 38(37%) cases, respectively. SBRT was delivered before chemotherapy (n=49,48%) or following first (n=31,30%) or further chemotherapy lines (n=23,22%). KRASmut was present ab initio in 49% of cases (n=50). Dose regimens included 48-60 Gy in 3-8 fractions, resulting in a median BED of 115.5 (range 76.8-151.2) Gy 10 . Median follow-up was 16 (range 2-45) months. Median LC was not reached; 1- and 3 years LC rates were 85% and 67% respectively (Fig.1A). At multivariate analysis (MVA), only a BED≤100Gy 10 (p=0.029, HR 2.99, IC95% 1.1- 9.5) and prior second or further chemotherapy line (p=0.031, HR 3.2, IC95% 1.1- 8.1) were independently correlated with impaired LC (Fig.1B-1C). Focusing on patients receiving no chemotherapy or first-line treatment before SBRT, 1- and 3 years LC rates were 92% and 77% respectively (median: NR; Fig.1D). At MVA, while BED≤100Gy 10 (p=0.036, HR 6.96, IC95% 1.9-25.7) was associated with poorer LC, lack of KRASmut (p=0.037, HR 0.26, IC95% 0.07- 0.9) was independently correlated with improved LC (Fig.1E-1F)

Median DFS and OS were 11 (95%CI 7-16) and 39 (95% 28-44) months (Fig.2A-2C). Improved DFS (15 versus 5 months, p=0.0003) and OS (39 versus 21 months, p=0.02) were observed in patients receiving no chemotherapy or first-line treatment before SBRT (Fig.2B-2D). No grade >2 toxicity was observed.